Charles Holland Duell (1880-1920), the commissioner of the United States Patent and Trademark Office from 1898 to 1901, supposedly told President McKinley in 1899 that the office should be abolished because “everything that can be invented has been invented.” However, there is no evidence that Duell ever said the line attributed to him.
 
“Everything that can be invented has been invented” was printed in Punch’s Almanack for 1899, but the anecdote involved a publisher’s office, not a patent office. In 1920, it was stated that an alleged letter from 1833 existed where someone resigned from the patent office because “everything that can be invented has already been invented.” In 1939, this incident was stated to have occurred in 1883. In 1957, the incident was given an 1836 date.
 
The 1899 Duell attribution has been cited in books and newspapers since 1976.
 
   
Wikipedia: Charles Holland Duell
Charles Holland Duell (April 13, 1850 – January 29, 1920) was the commissioner of the United States Patent and Trademark Office in 1898 to 1901, and was later a United States federal judge.
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In 1898, he was appointed as the United States Commissioner of Patents, and held that post until 1901. In that role, he is famous for purportedly saying “Everything that can be invented has been invented.” However, this has been debunked as apocryphal by librarian Samuel Sass. In fact, Duell said in 1902:
 
In my opinion, all previous advances in the various lines of invention will appear totally insignificant when compared with those which the present century will witness. I almost wish that I might live my life over again to see the wonders which are at the threshold.
 
Another possible origin of this famous statement may actually be found in a report to Congress in 1843 by an earlier Patent Office Commissioner, Henry Ellsworth. In it Ellsworth states, “The advancement of the arts, from year to year, taxes our credulity and seems to presage the arrival of that period when human improvement must end.” This quote was apparently then mispresented and attributed to Duell, who held the same office in 1899.
 
Google Books
Punch’s Almanack for 1899
Pg. XXXII:
THE COMING CENTURY.
SCENE—Office of a Publisher. Enter a Genius.
Genius. I want to seethe manager of the book department.
Boy. Oh there isn’t one, Sir.
Genius. Well, who looks after the pictures?
Boy. That’s done by machinery, Sir.
Genius. Isn’t there a clerk who can examine patents.
Boy. Quite unnecessary, Sir. Everything that can be invented has been invented.
Genius. Well, I want to leave a novel, a picture, and an idea.
Boy. You must be rather old-fashioned, Sir. All sorts of work is done, nowadays, by mental photography.
 
Google Books
May 1920, The Expositor and Current Anecdotes (Cleveland, OH), pg. 832, col. 2:
Forty Martyrs and Forty Crowns: Children’s Sermon
REV. W. DOUGLAS SWAFFIELD
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One of the most interesting buildings in beautiful Washington is the Patent Office. Here you might see the models of all the famous inventions which have been patented in the United States.  It is an even better place to visit than a great museum, because it tells the stories of how the dreams of many men and women have come true.  One day not long ago a letter was found in the office of this building which bore the date, 1833. The letter read something like this:
 
“Dear Sir: Because everything that can be invented has already been invented, it is inevitable that this office shall soon go out of business. Inasmuch as I will soon lose my (Pg. 834—ed.) position, I hereby resign to look for work elsewhere.”
 
“Yours truly,
“So-and-So.”
 
What a fool that young man was! There is always something new to be discovered, something great to be done, some good to be achieved. He lacked imagination.
 
16 March 1937, Illinois State Journal (Springfield, IL), “Dizzy Thinkers Say Dizzy World Needs Dizzy Things” (AP), pg. 1, col. 4:
They were suggested today by Herman A. Finke of St. Louis, an executive of the national inventors congress scheduled to open here March 29.
 
“So many people tell me that practically everything that can be invented has been,” he said. “In my opinion we have not scratched the surface.”
 
19 June 1939, Corona (CA) Daily Independent, “Truth about Advertising” by Charles B. Roth, pg. 1, col. 3:
Not one of us believe like the man who resigned from the U.S. patent office in 1883 because “everything that can be invented has been invented,” that we shall make no further progress; that there shall be no bette products for us to buy. We know there will.
 
25 June 1957, Star-News (Pasadena, CA), “They Just Pick & Choose” (editorial), pg. 8, col. 1:
In 1836, the director of the U.S. Patents office resigned and recommended to Congress that his office be done away with in the interest of economy. His reason was sincere, if unsound. The director said: “There is no further reason for a patent office because everything that can be invented has already been invented.”
 
21 June 1976, Augusta (GA) Chronicle, “The experts can often be incorrect” by Dr. Richard L. Lesher (U.S. Chamber of Commerce), pg. 4-A, col. 6:
In 1899, the director of the U.S. Patent Office urged President McKinley to close the office, because “everything that can be invented has been invented.”
 
24 February 1985, Wisconsin State Journal (Madison, WI), “Patent office keeping busy” (N.Y. Times News Service), sec. 4, pg. 9, col. 1:
WASHINGTON—“Everything that can be invented has been invented,” Charles H. Duell, commissioner of the Patent and Trademark Office, said to President McKinley in 1899.